Sydney University has locked down the prepaid function on the debit cards it issues to students as student IDs, after detecting a number of unauthorised transactions.

In an email distributed to students of the university, deputy vice-chancellor Professor Derrick Armstrong wrote that the university has put into place a $100 ATM cash-withdrawal limit for student debit cards as a precautionary measure.

The student cards can be used as an ANZ/Visa debit card, with students able to load almost $1000 onto the cards to make payments wherever electronic payments are accepted. Payment can be made using the card's magnetic strip or embedded chip, or by using Visa payWave. Students are only able to spend money that is "loaded" onto the card, and the student is required to opt in to use the feature.

Although students can normally load money onto their cards at kiosks in several locations, the university has temporarily barred the use of the cards at kiosks under its control; for example, in its libraries and recreational facilities. Loading money via BPAY or at 7-Eleven outlets is still accepted.

It has also temporarily barred the card from use in the university's libraries for printing and photocopying.

The university is working with ANZ to investigate the issue, and, in the meantime, has reminded students that they are able to make emergency cash payments via its Student Support Services facilities.